Calcium suppliments and snail shells
 

How important is it to add a calcium suppliment? I already add calcium once a week for fertilizing, I also add crushed coral which adds calcium to the water and there are a lot of empty snails in there to add it also. Is there any reason to add more or get something like calcium cabonate to add to the tank or should they have enough with what is in there on top of the romaine lettuce, fish food, zucchini and whatever else I feed them?

Calcium is very important. Your snails will develop shell erosion without it. If you have very hard water you may have enough calcium already. It can be as simple as adding a cuttlebone to the filter or tank, doesn't need to be anything fancy. You can also use calcium carbonate tablets from the pharmacy about once a month.